Compton scattering by the proton using a large-acceptance arrangement

Wolf, S.; Lisin, V.; Kondratiev, R.; Massone, Anna Maria; Galler, G.; Ahrens, J.; Arends, H. J.; Beck, R.; Camen, M.; Capitani, G. P.; Grabmayr, P.; Härter, F.; Hehl, T.; Jennewein, P.; Kossert, Karsten; L’vov, A. I.; Molinari, C.; Ottonello, P.; Owens, R.O.; Peise, J.; Preobrajenskij, I.; Proff, S.; Robbiano, A.; Sanzone, M.; Schumacher, M.; Schmitz, M.; Wissmann, F.

doi:10.1007/s100500170031

Cited by 36 publications

(56 citation statements)

References 51 publications

(173 reference statements)

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“…Then we fit the low energy data points varying only the bare polarizabilities. For the peak range, we use only the MAMI(2001) experiment [10], which contains 436 data points with photon incident energy ranging from 260MeV to 455MeV. A good fit is achieved at systematical uncertainty which tends to be large [53].…”

Section: Compton Scattering Cross Section and Polarizabilitiesmentioning

confidence: 99%

Proton Compton scattering in a unified proton-Δ+model

Zhang

Savvidy

2013

Phys. Rev. C

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We develop a field-theoretic model for the description of proton Compton scattering in which the proton and its excited state, the ∆ + resonance, are described as part of one multiplet with a single Rarita-Schwinger wavefunction. In order to describe the phenomena observed, it is necessary to incorporate both minimal and non-minimal couplings. The minimal coupling reflects the fact that the ∆ + is a charged particle, and in this model the minimal coupling contributes also to the γN ∆ magnetic transition. The non-minimal couplings consist of five electromagnetic form-factors, which are accessed at fixed and vanishing momentum-transfer squared with real photons in Compton scattering experiments, therefore it is possible to extract a rather well-determined set of optimal parameters which reasonably well fit the data in the resonance region 140-450 MeV. The crucial parameter which determines the γN ∆ transition amplitude and therefore the height of the resonance peak is equal to 3.66 ± 0.03, in units of µ N . We find that this parameter also primarily determines the contributions to magnetic polarizability in this model. In the low-energy region up to 140 MeV, we separately fit the electric and magnetic polarizabilities, while keeping the other parameters fixed and obtain values in line with previous approaches. The basic model is then extended with insights gained in the traditional approaches, namely incorporating the sigma-meson channel with the currently favored parameters, and the pion vertex corrections.

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Section: Compton Scattering Cross Section and Polarizabilitiesmentioning

confidence: 99%

Proton Compton scattering in a unified proton-Δ+model

Zhang

Savvidy

2013

Phys. Rev. C

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“…The HB O(e 2 δ 3 ) curves give a stronger cusp than the covariant version, but the HB O(e 2 δ 4 ) is in very good agreement with the covariant calculation up to 200 MeV and beyond. Though only low-energy data is used in the fit, the good agreement with the Mainz data [25] continues into the resonance region, though at most angles the Delta peak is somewhat too high. It should be noted though that in this region the power counting changes and the EFT calculation is only NLO.…”

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confidence: 92%

“…Using the Baldin sum rule to constrain their sum, we obtain αE1 = [10.6 ± 0. 25 The electromagnetic polarisabilities of the proton have been a subject of investigation for many years; the earliest extractions from low-energy Compton scattering data were carried out in the 1950s, and the relevant database was greatly expanded in the 1990s. In the very lowenergy regime one can make an expansion of the cross section which deviates from the Thomson scattering only through the inclusion of the two spin-independent polarisabilities α E1 and β M 1 .…”

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confidence: 99%

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Proton polarizabilities from Compton data using covariant chiral effective field theory

Lensky

McGovern

2014

Phys. Rev. C

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We present a fit of the spin-independent electromagnetic polarisabilities of the proton to lowenergy Compton scattering data in the framework of covariant baryon chiral effective field theory. Using the Baldin sum rule to constrain their sum, we obtain αE1 = [10.6 ± 0.25(stat) ± 0.2(Baldin) ± 0.4(theory)] × 10 −4 fm 3 and βM1 = [3.2 ∓ 0.25(stat) ± 0.2(Baldin) ∓ 0.4(theory)] × 10 −4 fm 3 , in excellent agreement with other chiral extractions of the same quantities.PACS numbers: 12.39. Fe, 13.60.Fz, 14.20.Dh The electromagnetic polarisabilities of the proton have been a subject of investigation for many years; the earliest extractions from low-energy Compton scattering data were carried out in the 1950s, and the relevant database was greatly expanded in the 1990s. In the very lowenergy regime one can make an expansion of the cross section which deviates from the Thomson scattering only through the inclusion of the two spin-independent polarisabilities α E1 and β M 1 . However, since very few measurements have been taken below 80 MeV, almost all extractions require theoretical input to describe the evolution of the cross section with energy. Historically, dispersion relation (DR) approaches were used, with input from pion photoproduction data. A model-independent constraint can be obtained from the Baldin sum rule, most recently evaluated to give α E1 + β M 1 = 13.8 ± 0.4 in units of 10 −4 fm 3 [1], so typically the parameter extracted is α E1 − β M 1 . In 2001 Olmos de León et al. published the most comprehensive data set yet, obtained with the TAPS detector at MAMI, and in a DR framework analysed it together with other "modern" data to give α E1 − β M 1 = 10.5 ± 0.9 ± 0.7 in the same units [1]. For some time this was regarded as the definitive result.However, chiral effective field theories (χEFT) can also be used to describe Compton scattering amplitudes. These are field theories in which the interactions of lowenergy degrees of freedom are governed by the symmetries of QCD, and scattering amplitudes can be systematically expanded in powers of the ratio of light to heavy scales. The former are typically external particle momenta of the order of the pion mass, and the latter are governed by those particles such as the ρ meson which are not included explicitly in the theory but whose effects, along with other short distance physics, are encoded in low energy constants. At leading one-loop order in the theory with pion and nucleons these predictions are parameter-free, but beyond leading order α E1 and β M 1 are free parameters which can be fit to data. The first attempt to do this was the work of Beane et al. [2,3], working in heavy baryon (HB) chiral perturbation theory. The absence of a dynamical Delta isobar restricted the fit to relatively low momentum transfer, and as a result the statistical errors were large. However, the inclusion of the Delta followed shortly [4][5][6]. Most recently, the result α E1 − β M 1 = 7.5 ± 0.7 ± 0.6 has been obtained by McGovern et al. in ref. [7]. Although this value is comp...

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“…The results of Refs. [36,37] are obtained using data above the pion-production threshold, while the result of Ref. [30] is extracted from the complete TAPS data set, ranging up to photon energies of 165 MeV.…”

Section: B Resultsmentioning

confidence: 99%

Proton scalar dipole polarizabilities from real Compton scattering data using fixed-t subtracted dispersion relations and the bootstrap method

Pasquini¹,

Pedroni²,

Sconfietti³

2019

J. Phys. G: Nucl. Part. Phys.

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We perform a fit of the real Compton scattering (RCS) data below pion-production threshold to extract the electric (αE1) and magnetic (βM1) static scalar dipole polarizabilities of the proton, using fixed-t subtracted dispersion relations and a bootstrap-based fitting technique. The bootstrap method provides a convenient tool to include the effects of the systematic errors on the best values of αE1 and βM1 and to propagate the statistical errors of the model parameters fixed by other measurements. We also implement various statistical tests to investigate the consistency of the available RCS data sets below pion-production threshold and we conclude that there are not strong motivations to exclude any data point from the global set. Our analysis yields αE1 = (12.03 +0.48 −0.54 ) × 10 −4 fm 3 and βM1 = (1.77 +0.52 −0.54 ) × 10 −4 fm 3 , with p-value = 12%. I. INTRODUCTIONThe electric and magnetic static scalar dipole polarizabilities, α E1 and β M 1 , respectively, are fundamental structure constants of the proton that can be accessed via real Compton scattering (RCS). In the low-energy expansion of the Compton amplitude, they correspond to the leading-order contributions beyond the structure independent terms that describe the scattering process as if the proton were a pointlike particle with anomalous magnetic moment. When approaching the pion-production threshold, also higher-order terms start competing with the scalar dipole polarizabilities. Therefore, one has to resort to reliable theoretical frameworks for extracting the scalar dipole polarizabilities from experimental data. The most accredited theories, which have been used sofar, are fixed-t dispersion relations (DRs), in the unsubtracted [1-3] and subtracted [4][5][6][7][8] formalism, and chiral perturbation theory (χPT) with explicit nucleons and Delta's, in the variant of heavy-baryon χPT (HBχPT) [9-11] and manifestly covariant [12,13] χPT (BχPT) 1 . Based on these theoretical frameworks, extractions of the scalar dipole polarizabilities have been obtained by fitting different data sets for the unpolarized RCS cross section, and adopting a statistical approach based on the conventional χ 2 -minimization procedure. Recently, a new statistical method has successfully been applied in Ref. [16] to analyze RCS data at low energies and extract values for the energy-dependent scalar dipole dynamical polarizabilities [17,18]. The method is based on the parametric-bootstrap technique, and it is adopted in this work to extract the scalar dipole static polarizabilities, using the updated version of fixed-t subtracted DRs formalism [8] as theoretical framework. Although the bootstrap method is rarely used in nuclear physics [16,[19][20][21][22], it has high potential and advantages [23]. In particular, we will show that it allows us to include the systematic errors in the data analysis in a straightforward way and to efficiently reconstruct the probability distributions of the fitted parameters. We will also pay a special attention to discuss the available sets of ...

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Compton scattering by the proton using a large-acceptance arrangement

Cited by 36 publications

References 51 publications

Proton Compton scattering in a unified proton-Δ+model

Proton Compton scattering in a unified proton-Δ+model

Proton polarizabilities from Compton data using covariant chiral effective field theory

Proton scalar dipole polarizabilities from real Compton scattering data using fixed-t subtracted dispersion relations and the bootstrap method

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